The general disposition of [14C]-Pranolium Chloride (SC-27761), a potential anti-arrhythmic agent, has been studied in the beagle dog, baboon and rhesus monkey. The compound was moderately absorbed from the gastro-intestinal tract of the three species at 5 mg/kg. There was appreciable inter-animal variation in the amount of absorption, and the absorption was dose-dependent in the monkey. After i.v. dosage the radioactivity was largely cleared via the kidneys. The initial elimination half-lives for Pranolium in the dog and primate were between 0.6 to 3.1 hours after i.v. dosage, but could not be determined after oral dosage. Less than 1% of the dose was localised in monkey fetal tissues, two hours after an i.v. dose was given to pregnant female rhesus monkeys, and the highest concentrations of radiolabel were detected in fetal liver. Pranolium was found to be extensively metabolised and 1-naphthol was identified as a major metabolite. Pranolium was excreted in urine both unchanged and as conjugates, but 1-naphthol was excreted largely as conjugates.